The present invention relates to a toe cap for a protective shoe and, more particularly, to a reinforced, injection molded plastic toe cap.
For many years, toe caps for protective shoes have been made of thin steel sheets formed into shoe toe-shaped bodies which are sewn or otherwise attached on the inside of the leather toe cap of a shoe or boot. Steel toe caps are known to deform under vertically applied compressive or impact loads and to undertake a permanent set which, if excessive, may result in a crushing and/or cutting injury to the toes of the wearer. Attempts have been made more recently to substitute various plastic materials for steel in safety toe caps and number of prior art patents show such constructions.
One of the more relevant prior art patents is Dykeman U.S. Pat. No. 4,735,003 which describes a molded plastic toe cap made of a variety of thermoplastic and thermosetting resins, both with and without fiber reinforcement. The body of the toe cap is provided with a flexible roof region, the deflection of which under load is intended to shift stresses to the lateral and forward wall regions which are generally heavier and more capable of supporting the loads. U.S. Pat. No. 4,735,003 describes the use of a number of possible molding techniques including injection molding. Also disclosed is the use of a polyurethane plastic with glass fiber reinforcement wherein the fibers have a length in the range of 1/4 inch to 1 inch as received from the plasticizing equipment and placed in a compression mold.
British Patent Application No. 2,138,272A also discloses a protective toe cap made from an injection molded glass-filled plastic material. The specification suggests that the flow rate of the plastic material and the gate size and location be chosen to ensure that there is no molding discontinuity or weakness in the upper portion of the toe cap. However, no injection flow rate nor gate size or location is specified.
European Patent Application No. 83304046.2 describes a protective toe cap for a shoe which is molded from a plastic material that is reinforced with uniaxially aligned continuous fibers extending laterally across the roof of the cap. However, the toe cap is molded using compression molding techniques and recognizes the need to carefully orient and hold the continuous fibers so that they are not dislodged from their position during molding. Injection molding techniques would not be suitable for the manufacture of this toe cap.
In the United States, suitability of toe caps for new protective footwear is determined in accordance with American National Standard for Personal--Protection Protective Footwear (ANSI Z41-1991). This Standard provides, inter alia, for separate compression and impact tests, both of which apply vertical loads to the roof of the toe cap actually installed in a shoe or boot. Similar but somewhat more rigorous standards are applicable in Canada under Canadian Standards Association toe impact test Z-195 March 1984. In Europe, the test regimen is dictated by DIN standards.
The rigorous test regimens to which protective toe caps are subject has it made extremely difficult to design and build a toe cap of either steel or plastic which will consistently meet any one of the standards, much less all of them. The problem is exacerbated by variations in toe cap styles in the United States and between the United States, Canada and Europe. These styles are, in turn, dictated to some extent by variations in the styles and in the construction of shoes, both work shoes and dress shoes which are modified to include protective toe caps. There is also a desire in the industry to eliminate steel toe caps for reasons in addition to those mentioned above, such as the heat and electrically conductive properties of steel. Also, the response of steel to magnetic or electrical signals makes it undesirable for certain military and the like applications.
Thus, there is a continuing real need in the industry for a plastic toe cap to replace steel toe caps which will meet the applicable test standards and still meet the aesthetic requirements of style, shape and relatively light weight. In addition, molded plastic toe caps should desirably be capable of being made at high production rates, such as by injection molding. It is known, however, that prior injection molding techniques and materials using fiber-reinforced plastics are subject to fiber degradation and difficulty in fiber orientation necessary to optimize the strength of the final product.